The present invention relates to a display and a display control circuit and, more specifically, to a display configured to perform overdrive processing on image data and a display control circuit.
One of problems in the display in recent years is an increase of transfer volume of the image data to a display panel driver for driving the display panel. For example, in liquid crystal displays in recent years, since resolution has improved and the frame rate has increased by adoption of double-speed driving (for example, the double speed to the quad speed), it is necessary to transfer a lot of image data to the display panel driver. In order to transfer the lot of image data, necessity of increasing a data transfer rate rises. However, if the data transfer rate is increased in order to transfer a lot of image data, there will arise problems that power consumption will increase and EMI (electromagnetic interference) will also increase.
In order to cope with the problem of the increase of the transfer volume of image data, the inventors are examining reducing the data transfer volume by transferring the image data after compressing it. Since this enables the data transfer rate to be made small, it becomes easy to reduce the power consumption and to do EMI measure.
One of other problems in the display is to make fast driving pixels of the display panel. For example, in the liquid crystal display in recent years, a load capacity of the liquid crystal display panel has become large by enlargement and higher resolution of the display. On the other hand, a frame rate has increased due to adoption of double-speed driving, and a time given to charge data lines of the liquid crystal display panel has shortened. For this reason, a technology of driving the pixels at high speed is being required.
One of the technologies for accelerating the driving of the pixels is overdriving. The overdriving is a technology of, when there is a change in the gradation value of the image data, driving the pixel so that a change in the drive voltage may become larger than an original change in the gradation value of the image data. Thereby, a response speed of the display panel can be raised.
One technique of realizing the overdriving is correcting the gradation value of the image data by data processing. Specifically, with reference to the gradation value of the image data of the previous frame, the gradation value of the original image data is corrected so that when the gradation value of the image data increases to be larger than that of the previous frame, the gradation value may become larger, and that when it decrease, the gradation value may become smaller. Hereinafter, such processing is called the overdrive processing.
The inventors consider that there is a technical advantage in providing a display corresponding to both the overdrive processing and compression processing. However, according to the inventors' finding, when the technology of transferring the image data after compressing it and the overdrive processing are used together, there may arise the following problems. The first problem is that when the overdrive processing and the compression processing are used together, the overdriving may be performed in an improper overdrive direction for each pixel due to an effect of a compression error. Here, the compression error is a difference between the gradation value obtained by uncompression processing and the original gradation value when the compression processing and the uncompression processing are performed on the original gradation value of the image data.
As shown in FIG. 1, when the compression processing and the uncompression processing are performed, a size relation between gradation values of the continuous two frames will be reversed to an original size relation, and therefore the overdrive direction may be set improperly. For example, suppose that the gradation values of specific subpixels of specific pixels of continuous three frames (here, they are termed as the first, the second, and the third frames) are 100, 124, and 120. In this case, originally, the gradation value of the second frame must be larger than the gradation value of the first frame and the gradation value of the third frame must be smaller than the gradation value of the second frame. However, if the compression error is in a range of ±4, this relation will collapse in the worst case. For example, if the gradation values after the compression processing and the uncompression processing become 104, 120, and 124, respectively, the gradation value of the third frame will become larger than the gradation value of the second frame. This means that the overdriving is done in an improper direction.
The second problem is that as shown in FIG. 2, the overdriving may be performed due to an effect of the gradation values of the surrounding pixels depending on the compression processing, although the overdriving is originally unnecessary. For example, let it be assumed that the gradation values of specific subpixels of the specific pixel take a constant value of 100 ideally among three frames. However, if the compression error arises due to an effect of gradation values of the surrounding pixels, unnecessary overdriving may be performed. For example, even when the gradation value after the overdrive processing is a constant value of 100 for a period of three frames, if the compression error is in a range of ±4, the gradation value after the compression processing and the uncompression processing will become 96, 104, and 96, which will be able to cause the overdriving to take place improperly. It is desired that these problems should be dissolved.
An image processing technology that performs both the overdrive processing and the compression processing is disclosed, for example, by Japanese Unexamined Patent Publication No. 2008-281734. In this technology, in order to make small a capacity of memory for storing the image data of the previous frame, the compressed data obtained by compressing the image data of the previous frame is stored in the memory. The image data obtained by uncompressing the compressed data stored in the memory is used for the overdrive processing. Furthermore, in order to reduce an influence of the error by the compression, the compression processing and the uncompression processing are performed also on the image data of the current frame, and the image data obtained as its result is used for the overdrive processing.
Furthermore, Japanese Patent Unexamined Application Publication No. 2009-109835 discloses a technology of performing the overdrive processing and also performing the compression processing on the image data of the current frame read from the memory for display and storing it in memory for overdrive.
However, in these technologies, it should be noted that the compression processing is performed in order to reduce a capacity of memory used for the overdrive processing. In other words, in these technologies, the compression processing must be performed before the overdrive processing. These two patent documents do not suggest a technology of transferring the compressed data obtained by performing the compression processing after performing the overdrive processing on the transmission side to the reception side, i.e., the display panel driver.